UKCCSRC Call 2 Project: Novel reductive rejuvenation approaches for degraded amine solutions from PCC in power plants

Aqueous amine scrubbing was originally developed for natural gas treatment and is currently considered to be the current best available technology for post-combustion capture (PCC) of CO2 from both pulverised fuel (PF) and natural gas combined cycle (NGCC) power plants. A major issue is the severe thermo-oxidative degradation of alkanomaine solvents that occurs in PCC compared to natural gas processing, with the problem being compounded by the presence of acid gases that lead to the formation of heat stable salts (HSS). The accumulation of degradation products is known to reduce CO2 capture efficiency and cause excessive foaming and fouling and unacceptably high corrosion rates. Current measures to compensate for degradation involves purging spent solvent solution for reclaimation, makeup with fresh amine and the addition of anti-foam and oxidation/corrosion inhibitors. Reclaimer technologies based on distillation, ion-exchange and elecrodialysis have been developed to deal primarily with HSS where distillation has the advantage of removing both the HSS and their anions (i.e. formate and acetate). However, these technologies do not deal with the majority of the other degradation products, particularly those arising from thermal and oxidative degradation. Further, it has generally recognised that MEA forms high boiling polymeric material where N-(2-hydroxyethyl)-ethylenediamine (HEEDA), in particular, may continue to degrade in the presence of CO2 to form longer substituted ethlyenediamines. This proposal has been prompted by our extremely promising preliminary results that the thermal and oxidative degradation of an amine polymer (polyethyleneimine) can largely be reversed using both hydrogenation and hydrothermal (hydrous) treatments. We used non-catalytic hydropyrolysis and hydrous pyrolysis treatments at temperatures below 250oC which were clearly effective in reducing oxygen functionalities without causing any degradation of the polymer chain. The challenge is to partially reduce degraded amines to hydroxyamines and also, for polymeric forms, to induce some hydrogenolysis to reduce chain lengths. Hydrous pyrolysis has the potential advantage of not directly requiring hydrogen with water being the hydrogen source. Judicious choice of catalysts provides selectivity for hydrogenation and hydrogenolysis and research on amine degradation in natural gas sweetening has shown degradation products, such as N,N-bis(2-hydroxy-ethyl)piperazine and N,N,N-tris(2-hydroxyethyl)ethylenediamine, can be converted back to hydroxyamines by a hydrotreating reactions . •Directly targeting a high research priority identified by the RAPID Handbook, the proposed research aims to investigate novel reductive approaches for rejuvenating spent amine solutions from PCC plants, namely selective catalytic hydrotreatments at modest temperatures and H2 pressures and hydrous pyrolysis (hydrothermal conversion). The specific objectives are: 1.To apply the hydrogenation/ hydropyrolysis and hydrothermal treatments to individual compounds, including 1-(2-hydroxyethyl)-2-imidazolidone (HEIA), HEEDA, .N-(2-hydroxyethyl)acetamide and N-methylformamide 2.Based on the model compound results, to conduct experiments on actual fractions from degraded amine solvents, notably the residues from distillation containing HSS and the compounds targeted above; and 3.To use the results to define the overall benefits hydrogenation, hydropyrolysis and hydrothermal treatments in solvent rejuvenation and a basis for planning the subsequent research needed to take forward these new treatments, in terms of identifying how these treatments can best be conducted continuously. Grant number: UKCCSRC-C2-189.

水溶性胺类洗涤技术最初是为天然气处理而开发的，目前被认为是从磨煤燃料（PF）和天然气联合循环（NGCC）发电厂中后燃烧捕获（PCC）二氧化碳的最佳现有技术。与天然气处理相比，PCC过程中烷基溶剂的严重热氧化降解是一个主要问题，这一问题因酸性气体的存在而加剧，酸性气体导致热稳定盐（HSS）的形成。降解产物的积累已知会降低二氧化碳捕获效率，并引起过度的泡沫和积垢，以及不可接受的腐蚀速率。当前的补偿降解措施包括对已用溶剂溶液进行排空以进行回收，用新鲜胺进行补充，以及添加抗泡剂和氧化/腐蚀抑制剂。基于蒸馏、离子交换和电渗析的回收器技术已被开发出来，主要处理HSS，其中蒸馏具有去除HSS及其阴离子（即甲酸和乙酸）的优势。然而，这些技术并未处理其他大多数降解产物，尤其是那些由热和氧化降解产生的产物。此外，普遍认为MEA形成高沸点聚合物材料，其中N-(2-羟基乙基)-乙二胺（HEEDA）尤其可能继续在二氧化碳的存在下降解，形成更长的取代乙二胺。本提议是由我们极其有希望的前期研究结果所引发的，即通过氢化和水热（含水的）处理可以很大程度上逆转胺聚合物的热和氧化降解。我们使用了低于250°C的非催化水热裂解和水热裂解处理，这些处理方法在明显减少氧官能团的同时，并未造成聚合物链的降解。挑战在于部分还原降解胺为羟基胺，对于聚合物形态，还需要诱导一些加氢裂化以降低链长。水热裂解具有不直接需要氢气，水作为氢源的潜在优势。谨慎选择催化剂提供了氢化和加氢裂化的选择性，对天然气脱硫中胺降解的研究表明，降解产物，如N,N-双（2-羟基乙基）哌嗪和N,N,N-三（2-羟基乙基）乙二胺，可以通过加氢处理反应转化为羟基胺。•直接针对RAPID手册确定的高研究优先级，本提议的研究旨在调查用于恢复PCC工厂用完的胺溶液的新型还原方法，即适度温度和H2压力下的选择性催化加氢处理和水热裂解（水热转化）。具体目标包括：1.将氢化/水热裂解和水热处理应用于单个化合物，包括1-(2-羟基乙基)-2-咪唑烷酮（HEIA）、HEEDA、N-(2-羟基乙基)乙酰胺和N-甲基甲酰胺；2.根据模型化合物的结果，对实际降解胺溶剂的份额进行实验，特别是含有HSS的蒸馏残渣和上述目标化合物；3.利用这些结果定义氢化、水热裂解和水热处理在溶剂再生中的总体效益，以及规划后续研究的基础，以确定如何最佳地进行这些新处理，从确定这些处理如何连续进行的角度来看。项目编号：UKCCSRC-C2-189。